The health benefits associated with polyunsaturated fatty acids [“PUFAs”], especially ω-3 and ω-6 PUFAs, have been well documented. In order to find ways to produce large-scale quantities of ω-3 and ω-6 PUFAs, researchers have directed their work toward the discovery of genes, the understanding of the encoded biosynthetic pathways that result in lipids and fatty acids, and genetic engineering techniques to introduce these biosynthetic pathways into preferred host organisms.
A variety of different hosts including plants, algae, fungi, stramenopiles and yeast are being investigated as means for commercial PUFA production. Genetic engineering has demonstrated that the natural abilities of some hosts, even those natively limited to linoleic acid [“LA”; 18:2 ω-6] or α-linolenic acid [“ALA”; 18:3 ω-3] fatty acid production, can be substantially altered to result in high-level production of various long-chain ω-3/ω-6 PUFAs.
Although the literature reports a number of recent examples whereby various portions of the ω-3/ω-6 PUFA biosynthetic pathway have been introduced into various hosts, significant efforts by Applicants'Assignee have focused on using the oleaginous yeast, Yarrowia lipolytica (formerly classified as Candida lipolytica). Oleaginous yeasts are defined as those yeasts that are naturally capable of or engineered to be capable of oil synthesis and accumulation, wherein oil accumulation is at least 25% of the cellular dry weight.
For example, U.S. Pat. No. 7,238,482 demonstrated the feasibility of producing omega-6 and omega-3 fatty acids in Yarrowia lipolytica. Intl. App. Pub. No. WO 2006/052870 demonstrated production of 28.1% EPA of total fatty acids in a recombinant Yarrowia lipolytica strain; U.S. Pat. No. 7,588,931 demonstrated production of 14% ARA of total fatty acids in a recombinant Yarrowia lipolytica strain; U.S. Pat. No. 7,550,286 demonstrated production of 5% DHA of total fatty acids in a recombinant Yarrowia lipolytica strain. And, U.S. Pat. Appl. Pub. No. 2009-0093543-A1 describes optimized recombinant Yarrowia lipolytica strains for EPA production and demonstrated production of up to 55.6% EPA of total fatty acids. In all of these methods, however, the production of PUFAs was demonstrated using oleaginous yeast grown using glucose as the carbon source.
It would be advantageous to produce PUFAs using carbon sources other than glucose, such as fructose and invert sucrose, because this would enable one to choose the most economical carbon source for a particular geographical region. For example, in regions such as South America, in particular Brazil, sugar cane is plentiful; therefore, invert sucrose would be an economical carbon source for the production of PUFAs.